A cogeneration system has conventionally been known that uses a gas engine and the like that runs on city gas and the like as an engine to supply electricity and heat. In such a cogeneration system, an electricity focused operation and a heat focused operation are performed. In the electricity focused operation, an operation pattern is determined in accordance with the electricity demand of an electricity consuming device such as lighting equipment. In the heat focused operation, an operation pattern is determined in accordance with the heat demand of the heat utilization device such as a freezer, a refrigerator, an air conditioner, and a water heater.
However, in both of the operations, the cogeneration system outputs heat and electricity at a certain ratio (hereinafter, referred to as “thermoelectric ratio”), regardless of the electricity demand and the heat demand. Therefore, in the electricity focused operation, if an amount of output heat is insufficient, the shortage portion needs to be compensated by additional electricity or a boiler, and if, on the contrary, the amount of the output heat is more than necessary, the surplus portion needs to be discarded. In the heat focused operation, if the amount of generated electricity is insufficient, the shortage portion needs to be bought from an external electrical system, and if, on the contrary, the amount of the generated electricity is more than necessary, the surplus amount is sold to the electrical system at a low cost.
Thus, a first technique has been known for optimizing the operation pattern to prevent the shortage and surplus of the generated electricity and the output heat (see, for example, Patent Document 1). In the first technique, the variations of the electricity demand and the heat demand over time are learned through a plurality of steps to predict patterns of the demands, and the operation pattern is determined on the basis of the prediction. Thus, the wasteful energy consumption is prevented, whereby the energy cost is reduced.
Moreover, techniques haven been known for driving a thermally driven heat pump and an electrically driven heat pump by means of the generated electricity and the output heat from the cogeneration system and the like (see, for example, Patent Document 2, Patent Document 3, and Patent Document 4). In a second technique described in Patent Document 2 and Patent Document 3 of the techniques, cooling of a refrigerant liquid is facilitated by means of cooling from a thermally driven heat pump to reduce the enthalpy of the refrigerant liquid, to thereby improve the freezing capacity. In a third technique described in Patent Document 4, operations of the thermally driven heat pump and the electrically driven heat pump are combined in such a manner that the output heat is appropriately increased/reduced in accordance with the variation of the heat demand over time, to thereby improve heat demand following capability.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. H8-14103.    [Patent Document 2] Japanese Unexamined Patent Application Publication No. H11-223412.    [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2003-121025.    [Patent Document 4] Japanese Unexamined Patent Application Publication No. H8-86533.